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Full text of "Alexander von Humboldt"

183                                   UFB   OF
light of the sun should discharge  a self-generated
While Humbolit was examining the magnetic
and luminous phenomena of the earth's interior^
he also observed the phenomena which the heat
of the earth had produced on the earth itself, and
on its formation. Here he arrived at his favourite
scheme of volcanic appearances. From the interior
heat he deduced the revolutions of the earth, the
former elevation of whole lands and mountains,
the formation of their strata and minerals, and of
the gaseous and fluid earths ; he recognised this inte-
rior warmth as the cause of the local changes of the
earth by vibration and eruption, such as the gushing
forth of hot springs, the rising* of oxygen or sulphur-
ous smoke, the ejection of volcanic matter, and the
eruption of volcanic mountains. In all these pheno-
mena, he sees only the reactionary activity of the in-
terior of the earth towards ijbs crust and surface. From
the remains and petrifactions of antediluvian life, he
judges that this reaction was formerly more powerful
than it is now, that the oxygen must then have been
discharged into the atmosphere more abundantly than
at present ; that it must, by the imparting of oxy-
gen to plants, have produced a fax more fertile vege-
tation ; and this is shown by the extinct traces of
former forests, the tremendous coal deposits, and
other bctried, "bttming materials. The earthquake —
that perpendicular, horizontal, or circular vibration of
the earth's surface and crust, which science can now
measure in direction and force with tolerable accu-
racy, which is accompanied by dull noises and subter-
ranean thunder, wMle the springs often dry and great
desolation is caused — this became, for Humboldt, an
important means to the knowledge of the earth. His
* Besides this aurora "borealis there  are other  forms of  terres-
trial light. Hnmboldfc includes. among them the y&t unexplained
•weather lights, the dry luminous fog- of 1783 and 1831, the steady
light of ^ large clouds which Rozier and Beccaria observed., the
bright nights of autumn and winter, &c,